Saturated hydrocarbon disproportionation at low temperatures

ABSTRACT

A process for disproportionation of saturated hydrocarbons which comprises contacting the saturated hydrocrarbons at a temperature below 850*F, and much more preferably below 800*F, and in the presence of no more than 5 weight percent olefin, with a catalytic mass having catalytic activity for dehydrogenation as well as catalytic activity for olefin disproportionation.

United States Patent 1191 Hughes 1 *Feb. 4, 1975 [54] SATURATEDHYDROCARBON 3,507,931 4/1970 Morris et al. 26()/683.65DISPROPORTIONATION AT LOW 3.773.845 9/1973 Hughes 260/676 R 3.775.50511/1973 Hughes 260/676 R TEMPERATURES [75] Inventor: Thomas R. Hughes,Orinda, Calif. [73] Assignee: Chevron Reseach Company, San Primary -f f5 6mm Francisco Calif Assistant bxammerluan1ta M. Nelson Attorney.Agent, or Firm-F. F. Magdeburget: R. H. Notice: The portion of the termof this i j [)6 Young patent subsequent to Nov. 27, 1990, has beendisclaimed.

[22] Filed: Aug. 1, 1973 [57] ABSTRACT [21] App1. No.1 384,853

Related U.S. Application Data A process for disproportionation ofsaturated hydro- {63] Continuation f Ser. No. 3,303,121 16, 1970.carbons which comprises contacting the saturated hydrocrarbons at atemperature below 850F, and much [52] U.S. Cl. 260/676 R, 260/683 D morepreferably below nd in the pre ence of 51 Int. Cl. C07c 9/00, C07c 3/00no more than 5 weight percent Olefin, with a catalytic [58] Field ofSearch 260/676 R, 683 D mass having catalytic activity fordehydrogenation as well as catalytic activity for olefindisproportionation. [56] References Cited UNlTED ST ES PATENTS 5 Claims,3 Drawing Figures 3,445,541 5/1969 Heckelsberg et al. 260/683 D so 3 sog CURVE a 55 CONVERSlON 3 g o J) it II 50 0 Lu O z 1 0 Lu 0 r CURVE A ,i*5 SELECTIVITY 4 1- (ULTIMATE YIELD OF c E j I) l l 1 l 650 700 750 B00B 900 TEMPERATURE, OF.

PATENIEDFEB 41% TOTAL CONVERSION, WTZ,

SHEET 1 OF 3 CURVE 'B CONVERSION (ULTIM CURVE A SELECTIVITY ATE YIELD OFC5+) TEMPERATURE, F.

FIG.1

ULTIMATE YIELD OF c +,wT.7,

PATENIEDFEB 4 3.864.417

sumaor 3 TEMPERATURE,F.

FIG 2 lci HWIJ. V/(NOISHEIANOO) 001 V=EIiVH ONl'lfiOd PATENTED FEB 75SHEET 3 UF 3 CURVE D CURVE B CURVE C CONVERSION oD- C5+YIELD -0-I- CURVEA 0 O O O O O O 8 7 6 5 4 3 2 b dwmI J: ME 31 It; a m 0% m2 51mm D E +3PROPYLENE IN hC4 FEED,WEIGHT F l G 3 SATURATED HYDROCARBONDISPROPORTIONATION AT LOW TEMPERATURES This is a continuation ofapplication Ser. No. 3,303, filed Jan. 16, 1970.

BACKGROUND OF THE lNVENTlON with different distributions of molecularweights than those ofthe feeds. More particularly, the present inventionrelates to disproportionation of saturated hydrocarbons.

The term disproportionation is used herein to mean the conversion ofhydrocarbons to new hydrocarbons of both higher and lower molecularweight. For example, a pentane may be disproportionated according to thereaction:

Saturated hydrocarbon as used herein includes hydrocarbon moleculeswhich are completely saturated with hydrogen and/or hydrocarbonmolecules which are partially saturated with hydrogen but contain atleast one alkyl group which is completely saturated with hydrogen. Thus,the term saturated hydrocarbon as used herein includes alkanes(paraffins); alicyclics (cycloparaffins); branched-chain alkanes;alicyclic hydrocarbons with one or more attached alkane groups; andunsaturated hydrocarbons with one or more attached, completely saturatedhydrocarbon groups, as, for example, an aromatic hydrocarbon with anattached alkane. From the description hereinbelow, it will becomeapparent that in the instance of unsaturated hydrocarbons with anattached, completely saturated hydrocarbon group the conversion processof the present invention operates by way of the completely saturatedhydrocarbon group.

2. Prior Art A number of processes have been disclosed for convertingvarious hydrocarbons to higher molecular weight hydrocarbons. Forexample, polymerization has been proposed for increasing the molecularweight of hydrocarbons such as gaseous, or low-boiling olefins. Variousprocesses for olefin polymerization have been disclosed, includingprocesses wherein the polymerization reaction is catalyzed withinorganic acids such as sulfuric or phosphoric.

To obtain the olefinic feed for a polymerization reaction, both thermalcracking and catalytic dehydrogenation processes have been proposed. Forexample, a two-stage process has been proposed wherein hydrocarbon gasesare first cracked to form substantial amounts of olefins. Then theolefins are polymerized to higher-boiling compounds by contacting theolefins with a catalyst adapted to promote the forming of heavierhydrocarbons by polymerization.

U.S. Pat. No. 1,687,890 is directed to a process of convertinglow-boiling point hydrocarbons into higherboiling point hydrocarbons bymixing a hydrocarbon vapor with steam and then contacting thesteamhydrocarbon mixture with iron oxide at temperatures in excess of1,112F. It is theorized in U.S. Pat. No. 1,687,890 that the followingreactions may be involved to a greater or lesser extent:

l. Paraffin hydrocarbons on being brought into contact-with ferric oxideat elevated temperatures are oxidized or dehydrogenated, formingunsaturated hydrocarbons.

2. Unsaturated hydrocarbons of low molecular weight polymerize intounsaturated hydrocarbons of higher molecular weight when subjected toelevated temperatures, the extent of polymerization depending upon thetemperature and duration of treatment.

7. Unsaturated hydrocarbons are hydrogenated by nascent hydrogen."

Another process which has been proposed for converting hydrocarbons tohigher molecular weight hydrocarbons is olefin disproportionation.Numerous methods and catalysts have been disclosed for thedisproportionation of olefins. In most of these processes, the olefin isdisproportionated by contacting with a catalyst such as tungsten oxideor molybdenum oxide on silica or alumina at a temperature between aboutand 1,100F and at a pressure between about 15 and 1,500 psia. Theseprior art processes have been directed to an effective method to convertessentially only olefins, not saturated hydrocarbons, to highermolecular weight hydrocarbons by disproportionation.

For example, in U.S. Pat. No. 3,431,316, an olefin disproportionationprocess is disclosed, and it is stated that, if desired, paraffinic andcycloparaffinic hydrocarbons having up to 12 carbon atoms per moleculecan be employed as diluents for the reacton; that is, the saturatedhydrocarbons are nonreactive and merely dilute the olefins which are thereactants.

A process for the direct conversion of saturated hydrocarbons to highermolecular weight hydrocarbons would be very attractive because in manyinstances saturated hydrocarbons are available as a relatively cheapfeedstock. For example, in many instances, excess amounts of propaneand/or butanes are available in an over-all refinery operation.

Processes which have been previously reported wherein saturatedhydrocarbons are disproportionated include contact of saturatedhydrocarbons with solid catalyst comprised of AlCl on A1 0 and contactof saturated hydrocarbons with a promoter comprised of alkyl fluorideand BF;,. The use of the AlCl solid catalyst was uneconomic because,among other reasons, the catalyst was nonregenerable. The use of alkylfluoride and BE, was unattractive because of severe corrosion, sludgeformation and other operating problems.

In the past it has been the practice to convert satu' ratedhydrocarbons, particularly normal alkanes, to olefins as a separate ordistinct step and then to disproportionate the olefins to valuablehigher molecular weight hydrocarbons.

For example, in U.S. Pat. No. 3,431,316, saturated light hydrocarbonsare cracked to form olefins, and then the olefins are separated from thecracker effluent and fed to a disproportionation zone wherein theolefins are disproportionated to higher molecular weight hydrocarbons.Thus, a separate step is used to obtain olefins, because, according tothe prior art, no economically feasible process is available for thedirect disproportionation of saturated hydrocarbons.

U.S. Pat. No. 3,445,541 discloses a processfor thedehydrogenation-disproportionation of olefins and paraffins, using acombined dehydrogenation and disproportionation catalyst. According toU.S. Pat. No.

3,445,541 a hydrocarbon feed which is either an acyclic paraffin oracyclic olefin having 3-6 carbon atoms is contacted with the catalyst atconditions of temperature and pressure to promote dehydrogenation anddisproportionation. It is said that the process can be carried out attemperatures between 800F and l,200F; however, the lowest temperatureused for processing a paraffin in accordance with any of the examples ofU.S. Pat. No. 3,445,541 is 980F, and typically the temperature used isbetween l,040F and l,l25F.

The high temperature process disclosed in U.S. Pat. No. 3,445,541 isshown therein to result in only relatively low yields of saturatedhigher molecular weight hydrocarbons. The U.S. Pat. No. 3,445,541process operates with a substantial amount of olefins in the reactionzone and thus with about to 50 volume percent or more olefins in theeffluent from the disproportionation reaction zone.

SUMMARY OF THE INVENTION According to the present invention, a processis provided for disproportionation of saturated hydrocarbons at atemperature below 850F, and much more preferably below 800F, and in thepresence of no more than 5 weight percent olefins, which processcomprises contacting the saturated hydrocarbons with a catalytic masshaving catalytic activity for dehydrogenation of hydrocarbon as well ascatalytic activity for olefin disproportionation.

More broadly, the present invention is directed to operating thesaturated hydrocarbon disproportionation zone in the presence of no morethan 5 weight percent olefins.

A catalytic mass comprising a physical mixture of catalyst particleswhich are active for dehydrogenation and catalyst particles which areactive for olefin disproportionation has been found to be effective fordisproportionation of saturated hydrocarbons when employed in accordancewith the present invention. In the process of the present invention, itis important that the two types of catalysts be in close proximity toone another. By close proximity is meant a distance less than a fewinches and preferably of the order of a few inches or less.

Ordinarily the dehydrogenation component will, of course, be adehydrogenation-hydrogenation component in accordance with standardprinciples of cataly- SIS.

Although not to be construed as a binding theory of operationrestricting the scope of the present invention or discovery, it isbelieved that the process may take place by virtue of the formation fromthe reactant saturated hydrocarbons of a relatively small amount ofolefins (reactant olefins) which migrate to the nearby active sites ofthe olefin disproportionation catalyst component and aredisproportionated to form different olefins (product olefins). Althougha method might be devised to withdraw the product olefins at this point,normally the product olefins are not withdrawn, but instead migrate toactive sites of the dehydrogenationhydrogenation component where theyare hydrogenated. It is believed that the success of the reaction of thepresent invention is partially due to a steady or continued removal ofthe product olefins formed in the reaction zone. The reactant olefinsformed as intermediates are disproportionated to form product olefinsand then product olefin removal is generally accomplished byhydrogenation of the product olefins, thus achieving a favorableequilibrium situation for the formation of additional reactant olefins,which olefins, in turn, may be disproportionated and hydrogenated in thereaction zone to form additional saturated product hydrocarbons ofmolecular weights other than that of the feed components, and so on.

It will, of course, be recalled that for most reversible or equilibriumlimited reactions (such as would be the case with the reactant olefinformation), the net rate of formation of product is increased bymaintaining low concentration of product in the reaction system, asopposed to a relatively high concentration of product in the reactionsystem. Thus, in the present process, it is believed that the netreaction rate of reactant saturated hydrocarbons to form reactantolefins is increased or maintained at a relatively high level by virtueof the fact that reactant olefins are constantly being consumed by theolefin disproportionation reaction which simultaneously occurs in thereaction zone. The product olefins formed by disproportionation are, inturn, maintained at low concentration in the reaction zone, preferablyby hydrogenation to product saturated hydrocarbons. This hydrogenationserves the additional function of consuming the hydrogen originallyproduced by dehydrogenation of the feed saturated hydrocarbons.

As a condition of operation of the present invention, it is criticalthat the olefin concentration be maintained relatively low; inaccordance with our present findings, the olefin concentration in thereaction zone is to be maintained below 5 weight percent. For purposesof the present invention, the olefin concentration in the reaction zoneis determined by analysis of the reaction zone effluent.

As discussed above, it is believed that one reason for the success ofthe process of the present invention is that the reactant olefins areconstantly being consumed by disproportionation and the product olefinsby hydrogenation to product saturated hydrocarbons, thereby establishinga favorable equilibrium situation and allowing further desired reactionin the reaction zone. We have found that it is undesirable to haveconsiderable amounts of olefin present in the reaction zone and that theaddition of olefin to the feedstock to the reaction zone will tend tokill the disproportionation reactions desired in accordance with theprocess of the present invention. This was a surprising finding,especially in view of the fact that it was initially thought that thedesired disproportionation of reactant saturated hydrocarbons to productsaturated hydrocarbons would be speeded up by the injection of suitableolefins into the disproportionation reaction zone. To the contrary,however, we have found that the addition of as little as one volumepercent olefin (specifically propylene) dramatically reduced theconversion of saturated hydrocarbons (specifically n-butane) to productsaturated hydrocarbon disproportionate. This is discussed furtherhereinbelow in conjunction with FIG. 3.

It is believed that the olefins are'detrimental to thedisproportionation reactions of the present invention because theolefins adsorb relatively strongly onto thehydrogenation-dehydrogenation catalytic sites and thus .prevent thesaturated hydrocarbon feedstock molecules from reaching these catalyticsites. In our laboratory work, we have noted that after the saturatedhydrocarbon disproportionation has been substantially inhibited by theinjection of olefins to the disproportionation reaction zone, most ofthe catalytic activity can be recovered by discontinuing the olefininjection to the reaction zone.

Other theories may be postulated as to why the presence of more than afew weight percent olefins in the reaction zone poisons the saturatedhydrocarbon disproportionation reaction of the present invention. Forexample, certain work by Wood, reported on page 30, Vol. 11 of theJournal of Catalysis (1968), indicates that the presence of adsorbedhydrogen is necessary for cyclohexane dehydrogenation to occur. Thisadsorbed hydrogen may be selectively scavenged by substantial quantitiesof olefins present in the disproportionation reaction zone, therebypreventing the saturated hydrocarbon feedstock molecules from beingdehydrogenated.

Whether because of a combination of the above theories, or one of thetheories separately, or some other theory, the finding remains that theprocess of the present invention requires that the concentration ofolefins in the disproportionation reaction zone be maintained at a lowlevel.

It is also preferred in the process of the present invention to operatethe reaction zone at a pressure above at least 100 psig. The elevatedpressure has been found advantageous because it leads to higherdisproportionation conversion. The residence time of the reactant in thereaction zone increases with increasing pressure. Also, the equilibriumpartial pressures of both olefin and H formed from dehydrogenation ofsaturated hydrocarbons rise in direct proportion to the square root ofthe total pressure. The equilibrium concentrations of olefins, relativeto those of the saturated hydrocarbons from which they are formed, areinversely proportional to the square root of the total pressure.Relatively high pressures, of the order of 500l,500 psig, areparticularly preferred.

While the process of the present invention requires that no more than 5weight percent olefins be present in the reaction zone, it is preferredto maintain the olefin concentration still lower as, for example, belowabout 2 weight percent olefins, and still more preferably, below about 1weight percent olefins. To maintain the olefin concentration at arelatively low level, various means may be employed. Temperatures belowabout 800F and elevated pressures above at least 100 psig areparticularly desirable to maintain the olefin concentration at arelatively low level in the disproportionation reaction zone. Inaccordance with one particularly preferred embodiment of the presentinvention, the temperature in the disproportionation reaction zone ismaintained below about 800F, the pressure is maintained above at least100 psig, and the olefin concentration is maintained below about 0.5weight percent.

Although it is advantageous to maintain the temperature in the reactionzone below about 850F and more preferably below about 800F in order tomaintain relatively low olefin concentration, it is also particularlyimportant to maintain the temperature below about 850F, and morepreferably below about 800F in order to obtain a relatively high yieldof saturated hydrocarbons which are of higher molecular weight than thefeed-saturated hydrocarbons. Thus, for example, when butanes or propaneare fed to the disproportionation reaction zone, a much better ultimateyield of C material is obtained when operating at the relatively lowtemperatures. Temperatures in the range of 500 to 700F are particularlydesirable. This aspect of the present invention is discussed hereinbelowin conjunction with FIG. 1.

Still further, the relatively low temperature, particularly below 800F,have been found by us to be extremely advantageous from the standpointof catalyst stability. That is, the fouling rates of catalysts used inthe process of the present invention have been found to be considerablylower when operating at the relatively low temperatures, i.e., belowabout 800F, as opposed to operating temperatures above 800F andparticularly operating temperatures above 850F. This as pect of thepresent invention is discussed further hereinbelow in conjunction withFIG. 2.

In a preferred embodiment of the process of the present invention, thecatalytic mass is comprised of catalyst particles having both catalyticactivity for dehydrogenation and catalytic activity for olefindisproportionation. In certain instances, rather than forming thecatalytic mass in the reaction zone by physical admixture of the twotypes of catalyst particles, it is more convenient and more desirable touse only one type of catalyst particle but, in accordance with theprocess of the present invention, this catalyst particle must havesubstantial catalytic activity for dehydrogenation as well as for olefindisproportionation.

Temperatures employed in the reaction zone usually are maintainedbetween 400 and 850F, preferably between 500 and 800F, and still morepreferably between 500 and 750F. Feed to the disproportionation reactionzone is preferably butanes and/or propane, as a large increase in thevalue of these particular hydrocarbon feedstocks is obtained by thedisproportion- .ation reaction.

Another particularly preferred feed is the highly paraffinic raffinateresulting from the extraction of aromatics from a portion of theeffluent from a catalytic reforming process. Typically, the raffinate ismostly C and C alkanes and has a relatively low motor fuel octanerating. By the disproportionation reaction of the present invention, theraffinate may be converted to higher octane light gasoline and to jetfuel.

The direct disproportionation of propane gives a relatively low yield ofC paraffins, whereas the yield from butanes is much higher.

As defined previously, the term saturated hydrocarbons is used herein toinclude a large number of types of hydrocarbons. However, the process ofthe present invention is preferably carried out using alkanes as thefeed-saturated hydrocarbons. As used herein, the term alkanes is used tomean hydrocarbons from the group of aliphatic hydrocarbons of the seriesC H excluding methane.

Feed hydrocarbons which are not converted in the disproportionationreaction zone preferably are recycled to the disproportionation reactionzone. Lower and higher molecular weight hydrocarbons formed in thedisproportionation reaction zone preferably are removed from theunconverted feed prior to recycling the unconverted feed. For example,generally all of the ethane formed is removed in the disproportionationof propane, or of propane plus butanes. The low molecular weighthydrocarbons are removed in order to prevent their accumulation in therecyclestream to the disproportionation zone.

the weight percent olefin added to a normal butane feed to adisproportionation reaction zone.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now in more detail toFIG. 1, the data tabulated below in Table I shows the yield of variousproducts for four different temperatures.

TABLE I Weight /1 Product Yields at Various Operating TemperaturesProduct 650F 700F 750F 800F 875F He CH, 0.2 0.2 0.5 1.1 3.2 C H 0.8 1.32.1 2.8 7.5 C l-1,. 5.9 11.6 15.7 19.8 16.0 iC H 0.1 0.l 0.2 0.4 0.5nC,H 83.1 67.7 56.7 46.9 53.1 E C H 0.5 0.4 0.5 0.5 N.M. Z branchedC;,H,. 0.06 0.1 0.2 0.5 0.8 nCsH 4.7 9.5 11.7 13.9 7.2 E C.-.H,., 0.10.1 0.2 0.2 NM. 2 branched C H 0.03 0.1 0.3 0.8 0.9 nC,,H 2.3 4.4 5.76.3 3.7 E C.,H, 0.1 0.1 0.2 0.4 N.M. X branched C H 0.009 0.05 0.2 0.30.6 nC;H 1.1 2.1 2.8 2.9 1.9 2 C H 0.02 0.05 0.08 0.06 N.M. E branchedC,.H 0.05 0.1 0.5 0.4 nC,.H,,. 0.5 1.0 1.3 1.3 1.0 E branched C,,H-,0.05 0.1 0.7 nC,.H 3 0.4 0.7 0.5 1 c,.,+ 0.3 0.5 2.0

.L C,C,-, 6.9 13.2 18.3 23 8 26.7 .2 9.4 18.4 24.2 28 4 19.7 Cr.+Ultimate Yield 57.7 58.3 56.9 54 4 42.4 E Olefins 0.7 0.8 0.9 1 2 1'l.M. [7r branched chain in C5-C9 range analyses are from an approximatechromatographic analysis.

so in branching with decreasing temperature indicates the process at thepresent Invention ls support. Thus, preferred catalyst masses includeplatinum-on-alumina particles mixed with tungsten oxideon'silicaparticles.

In accordance with one preferred embodiment of the present invention,the feed-saturated hydrocarbons consist essentially of, or at leastmostly of, just one carbon number saturated hydrocarbon such as propane;or normal butane with or without isobutane; or normal pentane with orwithout other C; carbon number saturated hydrocarbons such as thebranched-chain pentanes; however, mixtures thereof, i.e., mixtures ofany of the previously mentioned hydrocarbons, may also bedisproportionated. The term branched-chain is used herein to connotehydrocarbons such as Z-methylpentane or 2,2-dimethyl-butane, either ofwhich would be referred to in accordance with common practice asbranched-chain hexanes or branched-chain C alkanes.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graph showing the utimateyield ofC -lhydrocarbons versus temperature for the disproportionationof normal butane in curve A and percent total conversion versustemperature in curve B.

FIGJZ is a graph showing catalyst fouling rate versus temperature forthe disproportionation of normal butane.

FIG. 3 is a graph showing relative C yield versus Both catalystparticles were 28 to 60 Tyler mesh size. Operating Conditions:

Temperature: 650, 700, 750, 800, 875F Pressure: 900 psig Feed Rate: 9cc./hour Successive runs. of several hours each with no regeneration inbetween. were made at the temperatures specified. except that thecatalyst was reactivated by flushing the catalyst overnight withhydrogen before the run at 875F.

As can be seen from curve A in FIG. 1, the ultimate yield of C decreasesconsiderably in moving from particularly preferred temperatures below800F to temperatures in excess of 800F as, for example, temperatures ashigh as 875F where the ultimate yield of C -ldrops to about 42 percentversus approximately 57 percent at 750F.

The term ultimate yield" is used herein to mean the yield of thespecified material (e.g., C which would be obtained by recyclingunconverted feed back to the disproportionation reaction zone, assumingno loss occurs due to the recycling. In particular, the data points usedto obtain curve A in FIG. 1 are the calculated ultimate yield of Cmaterial, based on the amount of normal butane which was converted by asingle pass through the disproportionation reaction zone at the variousrespective temperatures. Thus, the ultimate yield of C is determinedfrom the single pass laboratory data by dividing the percent C yield bythe fraction of total conversion of the normal butane fed to thedisproportionation reaction zone. The fractional conversion of normalbutane includes. of course. the quantity of normal butane which wasconverted to lower molecular weight hydrocarbons, as well as thatportion of the normal butane which was converted to more valuable highermolecular weight hydrocarbons.

Curve B of FIG. 1 shows the total conversion of normal butane to thehigher and lower molecular weight products for single pass operationthrough the disproportionation reaction zone. The data for curve B wereobtained in essentially the same manner as that for curve A. The dataare tabulated in Table I. As can be seen from curve B, the conversionrises sharply in moving from relatively low temperatures such as 650F toreach a maximum at a point somewhere between 800 and 850F. However,although the conversion is higher, according to the graph, at atemperature somewhat in excess of 800F, it is clear that our findingsestablish that it is much preferable to operate at a temperature belowabout 800F in order to achieve relatively high yields of the valuablehigher molecular weight hydrocarbons. As the temperatures are raised upto 800F and above, the conversion goes up, largely because substantiallight hydrocarbons are generated, possibly due to cracking. However, atthe preferred operating temperatures of below 800F, there issubstantially greater ultimate yield of C material, as in indicated bycurve A of FIG. 1.

Furthermore, the relatively high olefin concentration in the productfrom the reaction zone when operated at 85 7F versus the relatively lowolefin concentration when operating at the lower temperatures, as can beseen from the data tabulated in Table I above, illustrates the advantageof operating the saturated hydrocarbon disproportionation zone in thepresence of no more than about 5 weight percent olefins and preferablysubstantially less olefins, as, for example, less than 1 weight percentolefins.

Results which are qualitatively similar to those shown in FIG. 1 wereobtained using a catalyst mass consisting of Pd on M 0 particles mixedwith W0 on SiO particles. These results are tabulated in summary form inTable II.

TABLE II Temperature 700 750 800 850 C,,+, ultimate yield 37 41.5 39 3|Deactivation rate 0.04 0.039 0.038 0.069 Pressure, psig 900 900 900 900LHSV' 1.0 1.0 L0 1.0 Feed nC nC nC, nC,

'Deactivation rate -d{log (conversion to C,+)}/dt, i.e.. thedeactivation rate is calculated as the rate of change (decrease) of thelogarithm of the per pass conversion to C,+ per unit time. e.g., perhour.

Temperature: 700, 800, 850F Pressure: 900 psig Feed Rate: 10 cc./hourLHSV: L0

Referring now in more detail to FIG. 3, it can be seen that theinjection of olef'tns to the disproportionation reaction zone isextremely detrimental when carrying out the disproportionation ofsaturated hydrocarbons. The reaction conditions used to obtain the datato plot curves A and B in FIG. 3 were obtained under essentially thesame conditions as described above with respect to FIG. 1, except thatvarying amounts of propylene were added to the normal butane feed andthe temperature was maintained at 650F for the data points of curves Aand B of FIG. 3. As can be seen from these curves, when operating thereaction zone at 650F both the conversion and the yield of valuable Chydrocarbons was substantially unaffected when only about 0.08 volumepercent propylene was added to the normal butane feed to thedisproportionation reaction zone. However, when about 0.4 volume percentpropylene was added to the normal butane feed, the C yield dropped about30 percent relative to what the C yield was prior to the addition ofpropylene to the normal butane feed. Still further, when about onepercent propylene was added, both the C yield and the conversion ofnormal butane dropped to about 10 percent of what the yield andconversion were when no propylene was added to the normal butane feed.

Thus, the data presented by curves A and B of FIG. 3 show that it isundesirable to have substantial amounts of olefins in the feed to thereaction zone and also indicates that it is preferable to operate thedisproportionation reaction zone in the presence of less than 1 weightpercent olefms when the disproportionation reaction is carried out attemperatures of about 650F or lower. We have found that somewhat higheramounts of olefins may be tolerated in the disproportionation reactionzone at higher temperatures. Thus, at temperatures of about 775F,somewhat greater amounts of olefins may be present without seriouslyretarding the saturated hydrocarbon disproportionation as is indicatedby curves C and D in FIG. 3. But it is important to maintain the olefinsbelow about 5 weight percent, and still more preferable to maintain theolefins at less than about 2 weight percent, in the disproportionationzone when operating at temperatures of about 750 to 800F.

In this respect, it can be calculated from dehydrogenation equilibriadata that at temperatures below about 800F the olefin concentrationresulting from a normal butane-olefin equilibrium is below about 2weight percent at 900 psig.

Although various embodiments of the invention have been described, it isto be understood that they are meant to be illustrative only and notlimiting. Certain features may be changed. It is apparent that thepresent invention has broad application to the disproportionation ofsaturated hydrocarbons. Accordingly, the invention is not to beconstrued as limited to thespecific embodiments or examples discussedbut only as defined in the appended claims.

I claim:

1. In a process for disproportionation of saturated hydrocarbons whichcomprises contacting the saturated hydrocarbons in a disproportionationreaction zone, with a catalytic mass having a component with catalyticactivity for alkane dehydrogenation and a second component withcatalytic-activity for olefin disporportionation, the improvement whichcomprises carrying out said contacting at a temperature between 400F and850F, and at an elevated pressure of at least 100 psig, and in thepresence of no more than weight percent olefins, and withdrawing fromthe disproportionation reaction zone product saturated hydrocarbonscontaining no more than 5 weight percent olefins.

2. A process in accordance with claim 1 wherein the improvement is madewhich comprises using as said 12 catalytic mass. a catalytic masscomprising catalyst particles having both catalytic activity fordehydrogenation and catalytic activity for olefin disproportionation.

3. A process in accordance with claim 2 wherein the catalytic masscomprises a physical mixture of (a) catalyst particles containing acomponent which has catalytic activity for alkane dehydrogenation, and(b) catalyst particles containing a component which has catalyticactivity for olefin disproportionation.

4. A process in accordance with claim 2 wherein the saturatedhydrocarbons consist essentially of alkanes.

5. A process in accordance with claim 4 wherein the saturatedhydrocarbons consist essentially of just one carbon number hydrocarbonselected from the group consisting of propane, normal butane, and normalpentane.

* k t at

1. IN A PROCESS FOR DISPROPORTIONATION OF SATURATED HYDROCARBONS WHICHCOMPRISES CONTACTING THE SATURATED HYDROCARBONS IN A DISPROPORTIONATIONREACTION ZONE, WITH A CATALYTIC MASS HAVING A COMPONENT WITH CATALYTICACTIVITY FOR ALKANE DEHYDROGENATION AND A SECOND COMPONENT WITHCATALYTIC-ACTIVITY FOR OLEFIN DISPORPORTIONATION, THE IMPROVEMENT WHICHCOMPRISES CARRYING OUT SAID CONTACTING AT A TEMPERATURE BETWEEN 400*FAND 850*F, AND AT AN ELEVATED PRESSURE OF AT LEAST 100 PSIG. AND IN THEPRESENCE OF NO MORE THAN 5 WEIGHT PERCENT OLEFINS, AND WITHDRAWING FROMTHE DISPROPORTIONATION REACTION
 2. A process in accordance with claim 1wherein the improvement is made which comprises using as said catalyticmass, a catalytic mass comprising catalyst particles having bothcatalytic activity for dehydrogenation and catalytic activity for olefindisproportionation.
 3. A process in accordance with claim 2 wherein thecatalytic mass comprises a physical mixture of (a) catalyst particlescontaining a component which has catalytic activity for alkanedehydrogenation, and (b) catalyst particles containing a component whichhas catalytic activity for olefin disproportionation.
 4. A process inaccordance with claim 2 wherein the saturated hydrocarbons consistessentially of alkanes.
 5. A process in accordance with claim 4 whereinthe saturated hydrocarbons consist essentially of just one carbon numberhydrocarbon selected from the group consisting of propane, normalbutane, and normal pentane.